Talk

What Causes the Rotation Period “Gap” in Young Clusters?

Sean Matt, University of Exeter

Period-mass diagrams of young clusters show a rotation period “gap," where stars are transitioning from being rapid rotators to converging onto a common slow-rotator sequence. A number of explanations for this gap have been put forward in the past few years. These explanations propose either dramatic transitions in stellar magnetism or wind driving, or they require that a substantial amount of angular momentum is hidden in the radiative core (due to “core-envelope decoupling”). It has not yet been shown whether any of these ideas can explain the morphology of the gap over its full mass range from ~0.1-1.0 solar masses. We show that the gap seen in young clusters is well explained by a simpler idea, which requires a relatively subtle flattening of the stellar wind torque as a function of rotation rate. Such a flattening could be caused by a systematic deficit (a sort of “super-saturation”) in magnetic field strength and/or mass loss rate, for faster rotators. Finally, since our model reasonably matches the spin-distributions for stars with and without radiative cores, it suggests that significant core-envelope decoupling may not be needed.